Muscle contraction is controlled by calcium ion which is sequestered and released from an intracellular organelle called the sarcoplasmic reticulum (SR). Little is known about the physiological process that initates and regulates the movement of calcium from the SR to the cytoplasm. It is proposed to use single skeletal muscle cells whose surface membranes have been removed by microdissection to study the mechanism of calcium release. An optical technique employing dyes which are sensitive to membrane potential will be used to follow the electrical effects of calcium movements and to deteremine if calcium release istriggered by voltage changes. The modulating influence of various physiologically significant ions on the release process will be studied. The information gaiend will add to our knowledge of the excitation-contraction coupling process in striated muscle.